The invention relates to a method of checking the presence of mobile stations communicating on a direct mode channel.
The invention is intended to be used in communication between radio equipments, such as mobile stations or radio phones.
Apart from system channels of radio telecommunications systems, direct mode channels can also be used, i.e. direct mode operation can be applied. Subscriber stations using direct mode operation do not communicate directly with a radio network or its base stations. Direct mode channels are frequencies at which the radio phones or other means of communication are able to communicate without the system directly with one another orxe2x80x94through repeater stationsxe2x80x94with the base stations of the system or with other mobile stations.
Direct mode channels are typically used in situations where e.g. a group of hand-held mobile phones communicate with one another at such a long distance from a base station that system channels cannot be used.
Another important use of direct mode channels is in the addition of capacity when traffic increases rapidly (incident) in one part of the service area of the system, e.g. at one point of the radio network.
A direct mode channel is also called a direct or simplex channel, or a simplex connection. A direct mode channel is a channel that is typically not used by the system at all. It may be, for example, a channel with the same channel spacing as the channels of the mobile system, e.g. 12.5 kHz or 25 kHz. Of the radio phones operating on a direct mode channel, a transmitting station has tuned its transmitter to the channel and transmits speech or data information. The other radio phones set to direct mode operation have tuned their receivers to the same channel, whereby they immediately hear the transmission.
On a direct mode channel, both analogue modulation and digital modulation can be used. A radio phone transmitting on the channel can also send signalling information, such as information about access rights, priorities, a group operating on the channel, or data traffic. On a direct mode channel, messages can be encrypted, or speech can be transmitted in clear form.
Subscriber stations operating in direct mode, i.e. on a direct mode channel, communicate with other subscriber stations on the direct mode channel without necessarily being in direct contact with the base stations of the radio network. They may, however, communicate with the radio network via repeater stations.
In normal direct mode channel communication, it is difficult for a (first) mobile station user to know which other mobile station users are on the direct mode channel, listening to possible transmissions of the first user. The problem appears when one wants to know whether a certain (second) mobile station and its user can be reached, i.e. whether the second mobile station hears the transmission of the first mobile station.
Another problem appears when one wants to know whether the transmission of the first mobile station is heard by a mobile station that should not hear it. Such an xe2x80x98unauthorizedxe2x80x99 mobile station is, for example, a stolen mobile station, a mobile station belonging to some other, undesired group, or an otherwise undesired mobile station.
The object of the invention is to provide a method of checking whether a desired mobile station is on a direct mode channel within the coverage area of the first mobile station and, if necessary, to check whether the user of the second mobile station is participating in a call or in communication on the direct mode channel.
It should be noted that a mobile station user can be a person using a mobile station or, alternatively, computer software using a mobile station for communication, or some other data processing application.
Another object of the invention is to provide a method by which it can be checked whether xe2x80x98unauthorizedxe2x80x99 or undesired mobile stations are listening to the transmissions of the first mobile station on a direct mode channel.
Yet another object of the invention is to provide a method by which the xe2x80x98unauthorizedxe2x80x99 or undesired mobile stations can be forced to stop communicating on the direct mode channel used by the first mobile station.
The objects of the invention are to be achieved without any communication between the users. Communication between the users is slow and not necessarily applicable to situations in which silence is required. It is naturally not possible to detect a stolen mobile station by an inquiry sent by the first mobile station user to the user of a second, stolen mobile station; a thief is unlikely to respond to an inquiry made on a direct mode channel.
The objects of the invention are to be achieved with minimal, short-term and, if necessary, secret communication on the radio path of a direct mode channel, so that the users of the other mobile stations communicating on the direct mode channel do not necessarily detect that a presence inquiry has been made.
A further object of the invention is to conduct a presence inquiry as quickly as possible to quickly ensure the safety of the direct mode channel.
A method of the invention for checking the presence of mobile stations communicating on a direct mode channel is characterized by the steps of: a) sending a presence inquiry message provided with an identity from a first mobile station to a second mobile station on the direct mode channel, b) receiving said presence inquiry message at the second mobile station, c) comparing the identity contained in said presence inquiry message with the identity of the second mobile station, d) if the comparison shows that the identities are identical, sending an acknowledgement containing the identity of the second mobile station from the second mobile station to the first mobile station on the direct mode channel, and e) indicating the result of the presence inquiry to the user of the first mobile station.
The invention also relates to a method of checking the presence of mobile stations communicating on a direct mode channel, the method being characterized by comprising the steps of: a) sending a presence inquiry message provided with an identity from a first mobile station to a second mobile station on the direct mode channel, the message containing negation data to be taken into account in a comparison made on the basis of the presence inquiry message, b) receiving said presence inquiry message at the second mobile station, c) comparing the identity contained in said presence inquiry message with the identity of the second mobile station, d) if the comparison shows that said identities are different, sending an acknowledgement from the second mobile station on the direct mode channel in response to said negation data and the comparison made in step c), the acknowledgement indicating the presence of the mobile station to the first mobile station, which has sent the presence inquiry message, and e) indicating the result of the presence inquiry to the user of the first mobile station.
The invention also relates to a mobile station communicating on a direct mode channel, the mobile station comprising: a transceiver, which is arranged to transmit and receive transmissions of a mobile station on the direct mode channel, memory means, a controller for controlling the operation of the mobile station.
The mobile station of the invention is characterized by comprising: transmission means for transmitting a presence inquiry message provided with an identity of a second mobile station to the second mobile station on the direct mode channel.
The invention also relates to a mobile station communicating on a direct mode channel, the mobile station comprising: a transceiver, which is arranged to transmit and receive transmissions of a mobile station on the direct mode channel, memory means, a controller for controlling the operation of the mobile station.
The mobile station of the invention is characterized by comprising: comparison means for comparing the identity contained in the presence inquiry message received by the mobile station with the identity of the mobile station, and acknowledgement transmission means, responsive to said comparison means, for transmitting an acknowledgement containing the identity of said mobile station to the mobile station that has sent the presence inquiry message.
The invention is based on the idea that when a first mobile station communicating on a direct mode channel wants to know whether other mobile stations or a certain mobile station is communicating on the same direct mode channel, the first mobile station sends a presence inquiry message on the direct mode channel. The message may contain the identity of a desired/paged mobile station, the identity of a group call group, or some other identity. The identity is received at the second mobile station communicating on the direct mode channel and is compared with the identity of that second mobile station. On the basis of the comparison, it is decided what the second mobile station will do next.
In a first embodiment of the invention, if the comparison shows that the identities are identical, the second mobile station sends the first mobile station an acknowledgement containing the identity of the second mobile station. From the acknowledgement the first mobile station learns that the second mobile station is communicating on the direct mode channel concerned. After receiving the acknowledgement, the first mobile station indicates the reception of the acknowledgement and its meaning to the user. Correspondingly, it is also possible to indicate it to the user if no acknowledgement is received at all during a certain time or certain time supervision. The user of the first mobile station can then conclude that the second, paged mobile station is not communicating on that particular direct mode channel.
In a second embodiment of the invention, negation data has been added to the presence inquiry message sent from the first mobile station, and the negation data is taken into account in the comparison made on the basis of the presence inquiry message. In response to the negation data and on the basis of the result obtained in the above comparison, if the comparison shows that the identity contained in the presence inquiry message sent by the first mobile station differs from the identity contained in the second mobile station, the second mobile station sends an acknowledgement on the. direct mode channel, indicating its presence to the first mobile station, which has sent the presence inquiry message. After receiving the acknowledgement, the first mobile station indicates the reception of the acknowledgement and its meaning to the user. Correspondingly, it is possible to indicate it to the user if no acknowledgement is received at all during a certain time or certain time supervision. The first mobile station can then conclude that the undesired second mobile station is not communicating on that particular direct mode channel.
The advantage of the solution provided by the invention is that the method and mobile station of the invention are also suitable for detection of stolen mobile stations, since the user of the second mobile station, i.e. the thief, does not necessarily even notice that the first mobile station is making a presence inquiry.
The invention can also be implemented such that the presence inquiry made by the first mobile station is indicated to the user whose presence is inquired, i.e. to the user of the second mobile station, and that the user can respond to the presence inquiry e.g. by pressing a key, i.e. a response can be given quickly without using speech.